:. >> brown: there are caveats. a number of caveats. tell us what we don't know about these planets and whether they're, in fact, suitable for life? hfrjts this is the $464 million question. do these planets that orbit their stars in orbits that remind us of the earth, the size of the earth, do they actually have liquid water? do they have lakes and oceans within which the biochemistry of life could flourish? do they have atmospheres that are conducive to life? do these planets have a moon that might stabilize the spin of their planets? so there could be properties of planets that render them suitable for life that we don't even know about. >> brown: and, of course, they're rather far away, right? so it's going to be hard to verify? >> well, one tragedy is that the stars we've been surveying are a thousand light years away. even traveling like that "voyager" spacecraft, it would take millions of years to get there. but the key is if one in five stars has an earth-like planet you only have to travel out a few light y